1. Field of the Invention
The present invention relates to noise and vibration suppressors. In particular, the invention relates to such suppressors for use in motor vehicles.
2. Summary of the Prior Art
Motor vehicles have components which, in operation, produce noise and/or mechanical vibration. In order to prolong component life it is desirable to reduce vibration and hence reduce the vibrational stress experienced by parts of the vehicle, including parts of the engine. Furthermore, it is also desirable to reduce noise produced in the motor vehicle, usually for environmental and comfort reasons. In the context of this application, vibration or mechanical vibration is to be taken to mean unwanted oscillatory movement of a solid, for example a component of a motor vehicle. Noise is to be taken to mean unwanted sound waves in air or other fluid. Of course, vibration can lead to the radiation of noise from a vibrating part, and noise can lead to the vibration of a part on which the noise impinges.
In particular, this invention is concerned with noise and/or vibration associated with a turbocharger (turbo) of a motor vehicle although it is not intended to be limited thereto. U.S. Pat. No. 5,979,598 discloses an intake silencer for a motor vehicle. This publication is concerned with reduction of noise (rather than vibration) caused by the intake of combustion air into an internal combustion engine. The intake silencer has a fixed axial sequence of resonator chambers of different volumes arranged around an intake pipe. Each resonator chamber communicates with the intake pipe through apertures in the wall of the intake pipe. Each resonator chamber and its apertures together form a Helmholtz resonator which can absorb noise in the intake pipe in a particular frequency range.
U.S. Pat. No. 5,979,598 discloses that the active absorption frequency of a Helmholtz chamber depends on the volume of the chamber. In order to obtain broadband silencing, the silencer has chambers of different volumes. Thus, the silencer as a whole will absorb noise in the intake pipe over a fixed envelope of frequency ranges, the individual noise frequency absorption ranges of the chambers being determined, at least in part, by the chamber volumes.
WO98/27321 discloses a noise suppressor formed by a plurality of modules in series. The modules define suppression chambers with particular noise suppression characteristics, and the chambers are designed so that different modules have different characteristics. Each module is self-contained. Respective ends of the noise suppressor are then connected to ends of a hose.